Device for reading out information stored in a phosphor-carrier, and an x-ray cassette

ABSTRACT

The invention relates to a device (10,60) for reading out information stored in a phosphor carrier (15) and to an X-ray cassette (70) which contains the phosphor carrier (15) and such a device. The inventive device (10,60) has a radiation source (11;20, . . . ,29,30 . . . 39; 50,53;61) that can emit a first radiation source (16) with which the phosphor carrier (15) can be exited such that the carrier emits a second radiation (17). This second radiation (17) comprises an image of the information stored in the phosphor carrier (15). The device (10,60) additionally has a receiving means (12,62) which contains a number of point elements (PD1, . . . PDn) in order to receive the second radiation (17) emitted from the phosphor carrier (15) in a point-by-point manner. The second radiation of a point of the phosphor carrier (15) can thus be received by each one of the point elements (PD1, . . . ,PDn).

BACKGROUND OF THE INVENTION

The present invention relates to a read-out device for informationstored in a phosphor carrier, and to an x-ray cassette. In particular,the present invention relates to a device for the line by line read outof information, such as x-ray information, stored in a phosphor carrier.The information is read out using a radiation source that can generateseveral individual beams, each of which stimulates the phosphor carriersuch that it emits secondary radiation. The secondary radiation, whichcontains at least a partial reproduction of the stored information, isreceived at a plurality of point elements of a receiving device. Thex-ray cassette includes the phosphor carrier and is designed for writingx-ray information onto this phosphor carrier.

Especially for medical purposes, x-ray radiation is used to generate animage of an object, for example a patient, where said image is stored asa latent image in a phosphor carrier. The phosphor carrier is stimulatedusing the radiation source to read out the x-ray image stored in thephosphor carrier. According to the stimulation, it will emit light withan intensity in proportion to the x-ray image stored in the phosphorcarrier. The light emitted by the phosphor carrier is received by adetection device, causing the x-ray image stored in the phosphor carrierto be made visible. For example, the x-ray image may be presenteddirectly on a monitor. On the other hand, it is possible to write thex-ray image on a photographic x-ray film specifically manufactured forx-ray images.

An apparatus for reading out information stored in a phosphor carrier isknown from the Published European Patent Application No. EP 0 777 148A1. In this known application, the phosphor carrier is stimulated by alaser beam. Using a very fast rotating polygon mirror and severaloptical lenses, the laser beam of a single laser is directed to thephosphor carrier. The apparatus described in the patent application is aso-called “flying spot” scanning device, where the laser beam reflectedby the polygon mirror stimulates all points of a line of the phosphorcarrier in sequence. The light emitted by the phosphor carrier due tothe stimulation with the laser beam is guided by a fiber cross-sectionconverter to a photoelectric sensor that converts the collected photonsinto electrical signals.

Using this apparatus, only one single point of the phosphor carriermaterial at a time is stimulated to emit light. To be able to read outthe entire information stored in the phosphor carrier in anacceptable—that is, a relatively short—time period, the individualpoints of the phosphor carrier can be stimulated only briefly. A typicalstimulation time for “flying spot” systems is about 6 μs for one point.Because of this brief time period of stimulation, the intensity of thelaser beam generated by the laser must be very high for the individualpoints of the phosphor carrier to be able to emit a sufficiently strongradiation. In addition, only a relatively small amount of the storedinformation can be read out. This limits the attainable quality forreproducing the stored information.

The laser beam stimulating the phosphor must fulfill certain conditionswith regard to spatial and spectral distribution. Such “flying spot”systems require a laser beam guidance with a length of 1.5 to 2 timesthe width of the line of the phosphor carrier that is to be stimulated,especially to be able to stimulate the entire width of the phosphorcarrier. Focusing and guiding the laser beam requires a verysophisticated and, thus, cost-intensive system of optical components.Furthermore, these optical components require considerable space suchthat the instrument dimensions of such a “flying spot” system are verylarge.

SUMMARY OF THE INVENTION

It is a principal objective of the present invention to ensure goodquality when reproducing information stored in a phosphor carrier.

This object, as well as other objects which will become apparent fromthe discussion that follows, are achieved, in accordance with thepresent invention, by providing a radiation source which includes anoptical device for expanding the several individual beams in thedirection of a line on the phosphor carrier.

According to the invention, the receiving device is designed such thatit contains a multitude of point elements and where the secondaryradiation emitted by the stimulated points of the phosphor carrier canbe received, point by point, simultaneously by several of these pointelements. A specified minimum energy E is required to stimulate theindividual points of the phosphor carrier such that they can emit thissecondary radiation. This energy is proportional to the power(intensity) of the radiation source and the dwell time of the primaryradiation emitted by the radiation source at the point of the phosphorcarrier to be stimulated. If several points of the phosphor carrier arestimulated at the same time, it is possible to attain a relatively longdwell time of the primary radiation for each point of the phosphorcarrier, without prolonging the overall time for reading out the entireinformation stored in the phosphor carrier. Moreover, it isadvantageously even possible to shorten this overall time for readingout the entire information stored in the phosphor carrier. Due to thelong dwell time at each point of the phosphor plate, the scanning speedfor stimulating the points of the phosphor plate can be kept low. Eachpoint emits a large secondary radiation that can be detected by thereceiving device.

It is possible to integrate the secondary radiation emitted by thephosphor carrier over a long time period. Since each point element ofthe receiving device exhibits a certain background noise, the signal tonoise ratio of the point elements can be increased advantageously basedon the invention. Due to the longer dwell time of the primary radiationof the radiation source per point of the phosphor carrier, it is alsopossible to reduce the power (intensity) that needs to be generated bythe radiation source and to still generate the required energy E forstimulating the phosphor carrier.

In an advantageous embodiment of the invention, it is possible tosimultaneously stimulate several points, in particular, all points thatare arranged in a line of the phosphor carrier. In doing so, it ispossible to stimulate a large number of points of the phosphor carriersimultaneously and at the same time keep the expenditures for the designof the radiation source and the receiving device relatively small. Thus,the required number of components in the radiation source and thereceiving device can be limited. This ensures a great compactness of thedevice.

Advantageously, several individual beams can be generated by theradiation source, which makes simultaneous and precise stimulation ofseveral points of the phosphor carrier simple and effective.

An advantageous design of the radiation source exhibits several laserdiodes that are used for the stimulation of the several points of thephosphor carrier. Laser diodes can generate sufficient radiation powerfor stimulating the points of the phosphor carrier. At the same time,they are very compact, such that they are conducive for the design withsmall dimensions of the device subject to the invention. In addition,laser diodes are easy to control.

In a particularly advantageous design of the invention, the number oflaser diodes in the radiation source is equal to the number of pointelements of the receiving device. In this case, each point of the lineof the phosphor carrier to be stimulated is stimulated simultaneously.The radiation source is then designed as a line of laser diodes. In thismanner, it is advantageously possible to do without additional opticalmeans for expansion and focussing of the laser diode beams. The distancebetween the radiation source and the phosphor carrier to be stimulatedcan be kept small, which further adds to the compactness of the device.

To be able to stimulate several points of the phosphor carrier with onesingle beam, the radiation source may be equipped with an optical systemwith which the single beam can be expanded in the expansion direction ofa line of the phosphor carrier. In this manner, it is alsoadvantageously possible to overlap several single beams, especially twosingle beams at least partially on the respective point of the phosphorcarrier to be stimulated. The stimulation power to be generated by theradiation source can be reduced using this overlapping of theintensities of several individual beams. Furthermore, the read-outreliability is increased in case one single beam malfunctions. To limitthe single beams despite the expansion in the expansion direction of onesingle line to this line, the optics provided in the radiation source isadvantageously designed such that it focuses the single beams in adirection perpendicular to the direction of expansion of the line. Thisensures that an unintentional stimulation of lines that are adjacent tothe line to be currently stimulated is avoided.

A reproduction device can be provided between the phosphor carrier andthe receiving device, which can be used to reproduce the secondaryradiation emitted by the individual stimulated points of the phosphorcarrier at the individual point elements of the receiving device.Advantageously, this reproduction is carried out on a 1:1 scale. In thismanner, the use of a fiber cross-section converter with itsdisadvantageously large dimensions can be avoided. This results in avery short distance between phosphor carrier and receiving device, whichin turn greatly improves the degree of compactness of the device.

Two radiation sources are provided in another particularly advantageousembodiment of the invention, where one receiving device each is assignedto said radiation sources. The two radiation sources and theirassociated receiving devices are arranged such that the phosphorcarrier, which is designed as a phosphor plate with a top and a bottomside, can be read out from both sides. This can further increase theamount of secondary radiation to be emitted by the phosphor carrier,which in turn improves the quality of the reproduction of theinformation that is to be read out from the phosphor plate.

According to the invention, a device for reading out information storedin a phosphor carrier is arranged directly in an x-ray cassette thatexhibits such a phosphor carrier. X-ray information stored in thephosphor carrier can then be read out directly from the device subjectto the invention and provided to a control device for furtherprocessing. Advantageously, such an x-ray cassette can be integrateddirectly in an x-ray unit. To read out the information stored in thephosphor carrier, it is advantageously no longer required for theoperating personnel to remove the x-ray cassette from the x-ray unit andinsert it in a special reading device for reading out the storedinformation. This significantly improves the operating convenience.

In one advantageous embodiment of the x-ray cassette subject to theinvention, a phosphor carrier is designed as a phosphor plate thatexhibits a top and a bottom side that have coatings that are differentfrom one another. These two different coatings exhibit differentsensitivities. For example, using the coating of one side of thephosphor plate, bones can be recorded better while the coating on theother side of the phosphor plate, may be better suitable to record softparts. This gives the operator the selection between two sensitivitiesbased on this design of the x-ray cassette subject to the invention.This allows for increased flexibility and capability of the devicesubject to the invention.

For a full understanding of the present invention, reference should nowbe made to the following detailed description of the preferredembodiments of the invention as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first exemplary embodiment of a device subject to theinvention for reading out information stored in a phosphor carrier inthe form of a reader head.

FIG. 2 shows another view of the first exemplary embodiment of thereader head subject to the invention.

FIG. 3 shows an example of a schematic presentation of the arrangementof the phosphor plate in lines and points.

FIG. 4 is a second exemplary embodiment of the device subject to theinvention.

FIG. 5 is a third exemplary embodiment of the device subject to theinvention.

FIG. 6 is a fourth exemplary embodiment of the device subject to theinvention with two reader heads.

FIG. 7 is an exemplary embodiment of an x-ray cassette subject to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be describedwith reference to FIGS. 1-7 of the drawings. Identical elements in thevarious figures are designated with the same reference numerals.

FIG. 1 shows the first exemplary embodiment of the device subject to theinvention for reading out information stored in a phosphor carrier. Areader head 10 is used to read out image information from a phosphorplate 15. X-ray radiation has been used to create this image informationin the phosphor plate 15. The reader head 10 exhibits a radiationsource, which is here designed as a line of laser diodes 11. The line oflaser diodes 11 is positioned perpendicular to the to the phosphor plate15 such that the radiation emitted by the individual laser diodesstrikes the phosphor plate directly. The line of laser diodes 11exhibits numerous laser diodes arranged next to one another, which, inthe present exemplary embodiment, can stimulate the entire width of therectangular phosphor plate that is capable of storing information. Here,the line of laser diodes contains 4096 laser diodes arranged parallel inone line next to one another.

Furthermore, the reader head 10 includes a receiving device, which, inthe present exemplary embodiment, is designed as “Charge Coupled Device”(CCD) line 12. This CCD line 12 exhibits numerous photo detectorsarranged parallel in one line next to one another. These photo detectorscan be used to perform a photoelectric conversion of a received lightradiation. They represent the point elements of the receiving device.Each photo detector can receive one light beam emitted from one of thestimulated points of the phosphor plate. Thus, 4096 photo detectors areprovided in the CCD line 12 of the present exemplary embodiment.

A reproduction device with so-called Selfoc lenses is provided betweenthe phosphor plate 15 and the CCD line 12. A Selfoc lens can be providedfor each stimulable point of the line of the phosphor plate 15, however,this is not required for the invention. Basically, the Selfoc lens is aglass fiber that exhibits a gradient in the refractive index towards thecenter. Due to a total reflection, it can transmit light in a bundledmanner practically without loss. Each Selfoc lens ensures that the angleof incidence of the light at the input of the Selfoc lens is the same asthe angle of deflection of the light at the output. Using a one-ortwo-dimensional arrangement of such Selfoc lenses, an area to bereproduced, that is assigned to this arrangement, can be reproducedprecisely at a 1:1 ratio onto an image area. Using a suitablearrangement of such Selfoc lenses, the light emitted by one of thestimulated points of the phosphor plate 15 can be reproduced in a simplemanner and very precisely on the assigned photo detector of the CCD line12. Micro lens arrays may be used in place of the Selfoc lenses.

At its output, the CCD line 12 is connected to a data processing unit13. The task of the data processing unit 13 is to evaluate and processthe electrical signals, generated by the CCD line 12 and containing areproduction of the image information stored in the phosphor plate 15,as well as to control the radiation source 11, particularly its advancefor line-by-line read-out of the phosphor plate 15. In the dataprocessor 13, the electrical signals generated by the CCD line 12undergo analog/digital conversion. Thereafter, the digital image dataobtained in this manner can then be processed by a digital signalprocessor using algorithms that have been stored in the data processingunit 13. In particular, the digital signal processor can calculatecorrection values and the individual digital image data of the imageinformation can undergo a correction procedure. In this manner, shortand long term fluctuations of individual components of the reader head10 subject to the invention or of the phosphor plate 15 can be takeninto account that would otherwise lead to errors or distortions whenreproducing the image information stored in the phosphor plate. Suchshort or long term changes may be, for example, performance fluctuationsof the laser diodes in use due to temperature fluctuations or aging. Itis also possible that the phosphor plate 15 has irregularities thatcould falsify the light radiation emitted by the phosphor plate 15. Itis possible to perform the corrections carried out by the dataprocessing unit 13 depending on the type of error to be corrected priorto each reading cycle or at greater intervals.

Due to the stimulation of several points of the phosphor plate 15according to the invention, particularly of all points of one of thelines of the phosphor plate 15, it is possible to provide a dwell timeof about 1 ms of the primary radiation per point of the phosphor carrier15. The power to be generated by one laser diode can then be about onemilliwatt.

The size of the line of the phosphor plate 15 and the size of itsstimulable points are determined by the cross-section of the laser diodebeam that stimulates the individual points of the phosphor plate 15 andby the size of the light-receiving area of the individual photodetectors.

During operation, the laser diode line 11 emits a primary radiation 16to stimulate the points of a line of the phosphor plate 15, where saidprimary radiation consists of 4096 individual laser diode beams based onthe laser diode line 11, which is made up of 4096 laser diodes. Thus,with these 4096 individual laser diode beams, 4096 individual points canbe stimulated to radiation in a line of the phosphor plate 15. The laserdiodes of the laser diode line 11 have a center-to-center distance ofabout 80 μm. An optical device for focusing the laser diode beams is notrequired because the distance between the laser diode line 11 and thephosphor plate 15 is very small (preferably<0.5 mm). The expansion ofthe individual laser diode beams is so insignificant that adjacentpoints of the phosphor plate 15 are generally not stimulated. Thus, thecenter-to-center distance of two laser diodes in the laser diode line 11basically corresponds to the distance between two stimulated points onthe phosphor plate 15.

The points of the phosphor plate 15 stimulated due to the primaryradiation 16 emit a secondary radiation 17 that is reproduced on theindividual photo detectors of the CCD line 12 by the Selfoc lenses ofthe Selfoc lens line 14. The CCD line 12 performs the photoelectricconversion of the received light emitted by the phosphor plate 15 in aknown manner and transmits the generated electrical signal containingthe reproduction of the image information stored in the phosphor plate15 to the data processing unit 13 for further processing.

By stimulating all points of a line of the phosphor plate 15, thebandwidth B is reduced, which in turn reduces the noise power P, whichis proportional to the bandwidth B according to the following equation:

P=4*k*T*B,

where T=absolute temperature and k=Boltzmann's constant.

FIG. 2 shows an additional view of the reader head 10 subject to theinvention according to the first exemplary embodiment. FIG. 2 shows anover-head view of the reader head subject to the invention and thephosphor plate 15. The reader head 10 is shown in a sectional view. Thereader head 10 spans the entire width of the phosphor plate 15 whereinformation may be stored. FIG. 2 shows schematically the laser diodeline 11 with laser diodes LD1 to LDn arranged parallel next to oneanother. Also shown is the CCD line 12 with photo detectors PD1 to PDnarranged parallel next to one another. In this exemplary embodiment, thelaser diode line 11 contains 4096 laser diodes and the CCD line 12contains 4096 individual photo detectors; thus n=4096. The reader head10 can be moved back and forth in a travel direction A. In this manner,the lines of the phosphor plate 15 can be scanned in sequence and theimage information stored in the various lines of the phosphor plate 15can be read out. Instead of the reader head 10, it is also possible todesign the phosphor plate 15 such that it can moved back and forth inthe travel direction A.

FIG. 3 shows an example of a schematic presentation of the division ofthe phosphor plate 15 according to lines and points of these lines asthey are specified according to the pattern of the sizes of thestimulating laser diode beams and the light-receiving areas of the photodetectors of the CCD line 12. A line length AZ specifies the length of aline of the phosphor plate 15 in the travel direction A of the readerhead 10. Here, this length AZ is determined by the cross-section of thestimulating laser diode beam. Here, the length AZ of the lines is about20 μm. At the same time, this line length AZ also specifies the lengthof one of the points of the line. A point width AP specifies the widthof a point of the line in the line direction B. Here, this width AP isspecified by the light-receiving area of one of the photo detectors ofthe CCD line 12. Here, it is about 80 μm.

Representing the lines of the phosphor plate 15, FIG. 3 shows fourconsecutive lines Z80, Z81, Z82 and Z83. The first line Z80 includesthree points 91, 92, and 93 among others. The second line Z81 includesthree points 101, 102 and 103, among others. The third line Z82 includesthree points 111, 112 and 113, among others, and the fourth line Z83includes three points 121, 122 and 123, among others. The points of thelines are arranged underneath one another such that they form variousrows P500, P501 and P502 of points that are all assigned to differentlines. In the example of FIG. 3, the points 91, 101, 111 and 121 arecontained in the first row P500, the points 92, 102, 112 and 122 in thesecond row P501, and the points 93, 103, 113 and 123 in the third rowP502. The points that are arranged in one of the rows underneath oneanother and that each belong to different lines are here designated asthe same points of the different lines.

To improve the signal-to-noise ratio, the intensities of the secondaryradiation from several points arranged underneath one another of severalneighboring lines can be integrated, i.e., combined, by the dataprocessing unit 13 after their stimulation. The mean value is thencalculated from these integrated intensities. This mean value thendetermines the reproduction of the points of the row combined in thismanner. In the present exemplary embodiment, the points of the fourlines Z80, Z81, Z82 and Z83 that are underneath one another in thevarious rows are combined. This means that the received radiationintensities of points 91, 101, 111, and 121 of the first row P500, thoseof points 92, 102, 112 and 122 of the second row P501, those of points93, 103, 113 and 123 of the third row P502, etc. are combined withsubsequent calculation of the mean value. In this manner, the samepoints, each with a length of 20 μm, of four lines are combined to one“large” point, which then exhibits a length of about 80 μm in the traveldirection A. The accepted disadvantage is that the resolution forreproducing the stored image information is reduced. However, theeffects of noise sources, such as the x-ray noise when writing to thephosphor plate, the light photon noise when reading out the phosphorplate or the phosphor plate noise can be reduced in this manner.

In place of a laser diode line that spans the entire width of thephosphor plate 15, it is also possible to use a radiation source withlaser diodes that stimulates only a portion of a line of the phosphorplate 15 to light. However, to read out the image information stored inthe entire line of the phosphor plate 15, it is then necessary to shiftthis radiation source in the expansion direction B of the line.

FIG. 4 shows a second exemplary embodiment of the device subject to theinvention. It exhibits numerous laser diodes 20 to 29 whose laser diodebeams S0 to S9 are reproduced on the phosphor plate 15 via reproductionoptical devices 30 to 39. Each one of the reproduction optical devicesis assigned to one laser diode. For simplicity's sake, the reproductionoptical devices can be realized using cylinder lenses, for example. Inthis exemplary embodiment, each laser diode 20 to 29 is used tostimulate several points of the phosphor plate. For this purpose, thereproduction optics device 30 to 39 assigned to their respective laserdiode 20 to 29 expands the respective laser diode beam S1 to S9 in theexpansion direction B of the line to be stimulated. FIG. 4 shows a line40 stimulated by the expanded laser diode beams S0 to S9. Furthermore,FIG. 4 shows a primary radiation field 41 representing the radiationfields of all laser diodes 20 to 29, where said radiation field, iscreated by the first laser diode 20 using the reproduction opticaldevice 30 assigned to this first laser diode 20. The reproductionoptical device 30 expands the laser diode beam S1 of the laser diode 20in the expansion direction B of line 40. Thus, a border of the primaryradiation field 41 runs on line 40 from a first point W to a third pointY. The laser diode beam S0 of the laser diode 20, which has beenexpanded by the reproduction optical device 30, is also focussed by thisreproduction optical device 30 in the direction A that is perpendicularto the expansion direction B of the line and that corresponds to thetravel direction of the reader head subject to the invention forscanning the phosphor plate 15. This ensures that only points of line 40that is to be stimulated is stimulated to light by the primary radiationfield 41. These points are located between the first point W and thethird point Y.

FIG. 4 also shows a second representative beam field 42, which iscreated by a second reproduction optical device 31 by expanding andfocussing an additional laser diode beam S1 that originates from aadditional laser diode 21. This additional laser diode beam S1 is alsoexpanded by optical device 31 in the expansion direction B of line 40and is focussed in the travel direction A of the reader head. Thus, thesecond beam field 42 stimulates those points of line 40 that are locatedbetween a second point X and a fourth point Z. The second point X islocated exactly in the center between the first point W and the thirdpoint Y.

This arrangement creates an overlapping field 43, where the first beamfield 41 and the second beam field 42 overlap. The intensity of theoverlapping field 43 is, therefore, approximetly twice is strong as theindividual intensities of the first and second beam fields 41 and 42,respectively.

The uniform arrangement of the individual laser diodes 20 to 29 and thereproduction optical devices 30 to 39 assigned to them ensures that eachpoint of line 40 that is to be stimulated is stimulated by the expandedand focussed laser diode beams of two laser diodes. In this manner, itis advantageously possible to increase the functional reliability ofthis radiation source, because a stimulation of all points of line 40that are to be stimulated is ensured even if one of the laser diodes 20to 29 were to malfunction. The intensity of the stimulating radiation ishowever reduced in the respective effected area if one of the laserdiodes 20 to 29 malfunctions, thus making detection of the malfunctionpossible. The data processing unit that performs the processing of thedigital image data after the receiving device detects and converts thelight into electrical signals can then correct the digital image datathat is erroneous due to the malfunction.

Alternative to the exemplary embodiment of FIG. 4, it is also possibleto overlap more than two laser diode beams on one point each of the lineto be stimulated. This can further improve the reliability in case ofmalfunction. Furthermore, the number of laser diodes of the radiationsource can be altered. It is not limited to ten laser diodes asdescribed in this exemplary embodiment.

FIG. 5 shows a third exemplary embodiment of the device subject to theinvention. In this third exemplary embodiment, the radiation sourceexhibits a thermal light source in the form of a halogen lamp 50.However, it is also possible to use a gas discharge lamp or any otherlight source with spontaneous light emission. The light of the halogenlamp 50 is coupled into a fiber cross-section converter 53 via a filter51 that provides a suitable adaptation of the wave length range used forthe stimulation of the phosphor plate 15. For this purpose, a thin glassfiber is coiled in one layer and roundly bundled at its one end 54. Theoutput area at the other end 55 of the cross-section converter 53 isadvantageously reproduced via a suitable optical unit in thereproduction plane on the line of the phosphor plate 15 to be stimulatedor is arranged closely above this line to be stimulated.

A shutter 52 that can be used to quickly and directly control thecoupling time of the light into the fiber cross-section converter 53 isprovided between the input of the cross-section converter 53 and thefilter 51.

A reason for using the halogen lamp 50 is that a high light power can beadvantageously achieved. Furthermore, this halogen lamp 50 can also beused to erase a phosphor plate 15 that has previously been written tousing the x-ray.

Instead of the use of a thermal light source, such as the halogen lampof the third exemplary embodiment, or the use of laser diodes accordingto the first and second exemplary embodiment, a filament lamp may beused as the radiation source, where the filament is used as the beamemitting area. Using a suitable spectral filter, the emitting area ofthis filament can be reproduced in the flat phosphor plate withoutadditional optical conversion. This can result in a very compact design.However, with regard to its emission properties, the filament lamp mustmeet the requirements concerning line width, length and uniformity ofthe area of the phosphor plate with the points to be stimulated.

Furthermore, it is also possible to use so-called light emitting diodes(LED), if they achieve sufficient emission energy. Advantageously, LEDscan also be used in the line form.

FIG. 6 show a fourth exemplary embodiment of the device subject to theinvention. In this exemplary embodiment, the phosphor plate 15 isprovided with a first coating on its top side 65, where this firstcoating differs from a second coating that is applied to the bottom side66 of the phosphor plate 15. The coatings of the top side 65 and of thebottom side 66 of the phosphor plate 15 have sensitivities that aredifferent from one another. In this manner, x-rayed objects that exhibitsignificantly different contrasts such as bones and soft parts, forexample, can be reproduced with very good quality using the samephosphor plate.

The device subject to the invention according to FIG. 6 exhibits tworeader heads 10 and 60 for reading the phosphor plate 15. In theirdesign, the two reader heads 10 and 60 correspond to the that of readerhead 10 that has already been described above based on the firstexemplary embodiment according to FIGS. 1 and 2. Thus, the two readerheads 10 and 60 each exhibit a laser diode line 11 or 61, respectively,for stimulating the points of the phosphor plate 15. Furthermore, theyeach contain a CCD line 12 or 62, respectively, for receiving theradiation emitted by the stimulated points of the phosphor plate 15 withthe radiation being reproduced on the associated CCD lines 12 or 62,respectively, using a Selfoc lens line 14 or 64, respectively. Theelectrical signals being generated by the two CCD lines 12 or 62,respectively, and containing a reproduction of the image informationstored in the phosphor plate 15 are transmitted to a common dataprocessing unit 63. This data processing unit 63 controls thefunctionality of the two reader heads 10 and 60. For example, it mayspecify whether one of the two reader heads, 10 or 60 or both togetherare to be used to read out the image information contained in thephosphor plate 15. The electrical signals transmitted by the two CCDlines 12 and 62 are combined in the data processing unit 63 to a totalimage. In doing so, the two signals may be weighted differently.

Through the possibility of reading out on both sides of the phosphorplate 15 an additional improvement of the reproduction of the read outimage information can be achieved. The main reason for this is simplythat more information stored in the phosphor plate can be read out.Advantageously, the scattering of the stimulation radiation that isgenerated when the stimulation radiation enters the phosphor plate 15that is coated on both sides can be kept small in comparison to a singlereader head that is located on one of the sides of the phosphor plate 15and that reads the image information from the phosphor plate that iscoated on both sides. This can significantly reduce the blurring of theread out image information due to scatter radiation.

The radiation sources described above for stimulating the individualpoints of the phosphor plate 15 can also be used in place of the twolaser diode lines 11 and 61.

FIG. 7 shows an exemplary embodiment of an x-ray cassette 70 subject tothe invention that exhibits a device subject to the invention forreading out information stored in a phosphor carrier. In the presentexemplary embodiment, the reader head 10 that has already been describedabove based on the first exemplary embodiment under FIGS. 1 and 2constitutes such a device subject to the invention. The x-ray cassette70 subject to the invention additionally exhibits the phosphor plate 15,where the information that is to be read out by the reader head 10 canbe stored. Guide bars 71 and 72 that supply the drive and guidance ofthe reader head 10 are provided along the two longitudinal sides of thephosphor plate 15. Advantageously, the reader head 10 may be driven by alinear motor 73 such that the reader head can be guided line by lineacross the phosphor plate 15 in the travel direction A. A control device75 is provided in the x-ray cassette for the precise control of thelinear motor 73 drive. Here, the two guide bars 71 and 72 are used asreaction components for the linear motor 73. By using the linear motor73 for the drive of the reader head 10, the use of complex powertransmission from a conventional electrical motor with a rotating shaftto the reader head 10 that causes inaccuracies can be avoided.

An erasing lamp 74 that is also guided across the phosphor plate 15 bythe linear motor 73 in order to erase image information stored in thephosphor plate is provided alongside behind the reader head 10.Advantageously, the reader head 10 and the erasing lamp 74 are movedacross the phosphor plate 15 by the same linear motor 73.

Such an x-ray cassette subject to the invention can be inserted directlyinto a x-ray table such that removal of the x-ray cassette for readingout the image information stored in it is not required. The x-raycassette 70 exhibits interface ports that can be used to transferdigital data generated in the reader head 10 to a monitor or printer.

Due to the design subject to the invention of the device for reading outinformation stored in a phosphor carrier, the x-ray cassette can bemanufactured with very small dimensions. It is possible to limit thethickness of the x-ray cassette to about 45 mm such that it can even beinsertable in conventional x-ray units already in operation.

There has thus been shown and described a novel device for reading outinformation stored in a phosphor carrier, and an x-ray cassette, whichfulfills all the objects and advantages sought therefor. Many changes,modifications, variations and other uses and applications of the subjectinvention will, however, become apparent to those skilled in the artafter considering this specification and the accompanying drawings whichdisclose the preferred embodiments thereof. All such changes,modifications, variations and other uses and applications which do notdepart from the spirit and scope of the invention are deemed to becovered by the invention, which is to be limited only by the claimswhich follow.

What is claimed is:
 1. In a device for the line by line read out ofinformation stored in a phosphor carrier with a radiation source thatcan generate several individual beams, for emitting a primary radiationthat can stimulate the phosphor carrier such that it emits a secondaryradiation that contains at least a partial reproduction of the storedinformation, and a receiving device for point by point reception of thesecondary radiation emitted by the phosphor carrier, wherein thereceiving device includes a multitude of point elements and wherein thesecondary radiation that is emitted by the phosphor carrier can bereceived at the same time by a plurality of these point elements, theimprovement wherein the radiation source includes an optical device forexpanding the several individual beams in the direction of a line on thephosphor carrier.
 2. The device as set forth in claim 1, wherein theradiation source includes a light source with spontaneous light emissionand a fiber cross-section converter.
 3. The device as set forth in claim2, wherein the light source is a halogen lamp.
 4. The device as setforth in claim 2, wherein the light source is a gas discharge lamp. 5.The device as set forth in claim 1, wherein the optical device focusesthe individual beams in a direction (A) perpendicular to the direction(B) of a line.
 6. The device as set forth in claim 1, further comprisingreproduction means, located between the phosphor carrier and thereceiving device, for imaging the secondary radiation emitted by theindividual points of the phosphor carrier in a ratio of 1:1 on theindividual point elements.
 7. The device as set forth in claim 1,wherein said device includes two radiation sources and two receivingdevices that are arranged such that the information stored in thephosphor carrier, which comprises a phosphor plate having a top side anda bottom side, can be read out both from the top side and from thebottom side of the phosphor plate.
 8. The device as set forth in claim1, wherein said device includes an evaluation means for evaluating thesecondary radiation that is received point by point by the receivingdevice, wherein said evaluation means includes means for combining theintensities of the secondary radiation of the same points of severaladjacent lines that have been read out and received point by point, andfor calculating a mean value of such intensities.
 9. An X-ray cassettefor writing to a phosphor carrier contained in the cassette, theimprovement wherein the cassette includes a radiation source foremitting a primary radiation that can be used to stimulate the phosphorcarrier such that it emits a secondary radiation for line-by-line readout of information stored in the phosphor carrier, wherein saidsecondary radiation contains at least a partial image of the storedinformation, and wherein the cassette includes a receiving device forpoint-by-point reception of the secondary radiation emitted by thephosphor carrier, wherein the receiving device contains a multitude ofpoint elements and where the secondary radiation emitted by the phosphorcarrier can be received by several of these point elements at the sametime.
 10. The X-ray cassette as set forth in claim 9, wherein thephosphor carrier comprises a phosphor plate having a top side and abottom side, and wherein the top side has a coating that is differentfrom that on the bottom side.
 11. The X-ray cassette as set forth inclaim 9, wherein the cassette includes a linear drive for moving theradiation source and the receiving device across the phosphor carrier.12. The X-ray cassette as set forth in claim 11, wherein the cassetteincludes an erasing device for erasing the information stored in thephosphor carrier, and wherein the erasing device is arranged such thatit can be moved across the phosphor carrier by the linear drive.
 13. TheX-ray cassette as set forth in claim 11, wherein the linear driveincludes an electric motor.